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Every now and then, you'll hear some ordinary household product or comestible touted as the "secret" ingredient in a homemade garden remedy.

Greener lawns! Bigger tomatoes! Madly blooming roses! Who wouldn't be intrigued to think that the greatest growth enhancer since barnyard manure is lurking in your cupboard, refrigerator or medicine cabinet?

Take Epsom salt, for example. I received annual press releases from the Epsom Salt Industry Council (yes, such a thing really exists), promoting the use of this product in the garden. They hook you by suggesting that Epsom salt will put an end to vexing problems like tomato and pepper leaves that turn yellow, lawns that turn brown and roses that turn into thorny nuisances with nary a flower.

This has me saying "hmmmm," since yellowing tomato leaves can have several causes, including bacterial and viral disease, and lawns (like mine) that are never irrigated go dormant and turn brown in hot, dry weather, no matter what you do. And what if your roses are the old-fashioned, once-blooming kind, genetically programmed to produce just a single, spectacular flush of flowers?

The council recommends dosing your lawn, your houseplants and your tomatoes (“a tablespoon in the planting hole and repeat applications every two weeks”) with Epsom salt, a product better known for soothing aching feet. Use it on evergreens, feed it to trees and offer perennials a healthy shot of it to force them into bloom!

The theory is that this highly soluble preparation aids in the absorption of nitrogen and phosphorous — two essential plant nutrients — and boosts the production of chlorophyll, the green stuff in plant leaves responsible for photosynthesis. I'm quoting here: "Epsom salt can help restore essential nutrients to the soil."

To investigate this claim, it helps to have someone like Jeff Gillman, an associate professor of horticultural science at the University of Minnesota and author of the handy book, "The Truth About Garden Remedies: What Works, What Doesn't and Why" (Timber Press).

It doesn't hurt a bit that the eminent plantsman Michael Dirr, advisor to Gillman during his doctoral studies, has written the foreword, and Ken Druse, the highly regarded garden author, has provided a back-of-the-book tout. The 15-page bibliography isn't bad, either, as proof that our guy has done his homework.

Proper application of Epsom salt thestaciesutra/flickr

Gillman points out that Epsom "salt" is a misnomer, since the principal ingredients are magnesium and sulfur. It isn't remotely related to table salt (sodium chloride), although it resembles a coarse, kosher salt in appearance. The "Epsom" part memorializes the locale in England where this product was first collected from naturally occurring mineral springs, by the way.

Epsom salt won't really do a thing for plants growing in soil that already has a sufficient supply of magnesium and sulfur — which is the case nearly everywhere. Where magnesium is low, soils are likely to be acidic, Gillman says. There is no real evidence that Epsom salts would change soil pH.

If conditions are too acidic for what you want to grow (vegetables, for instance, which prefer a "sweeter," or more alkaline, soil), dolomitic lime is a more appropriate supplement. It contains magnesium and actually will push acidic soil toward the alkaline end of the pH scale.

How would you know if you have the peculiar condition of true deficiencies in either magnesium or sulfur? You can't tell by looking. The only real way to go is to have your soil tested by a competent lab. You can do this by visiting your county office of the Rutgers Cooperative Extension Service and purchasing a kit that includes instructions and a mailing envelope addressed to their laboratories.

"By applying something, such as Epsom salt, without testing your soil, you are simply rolling the dice to find the cure," Gillman writes. "You may be right, but you may make things worse."

I've also seen Epsom salt recommended as a "cure" for blossom-end rot, a malady of tomatoes that causes them to rot at the base. This is nonsensical, since the condition is caused by a lack of calcium and/or inadequate watering. Lime will add some calcium to the soil; Epsom salt obviously will not.

Bottom line: "Epsom salts are not magic and don't take the place of other nutrients," Gillman says.

It's not bad for soaking your feet, though, after a long, hard day in the garden. Epsom salt is readily absorbed through the skin, and has a soothing and softening effect on your tootsies.Don't drink the stuff, though, unless you are having what the commercials delicately refer to as "irregularity." According to the council, it's an FDA-approved laxative.

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